1. Field of the Invention
The present invention relates to cooling devices and processes and, more particularly, to the cooling of subjects in order to produce such physiologic conditions as comfort or hypothermia.
As is well known, heat transfer occurs in several ways, of which the three most commonly considered are conduction, convection and radiation. A person immersed in a pool of cold water loses heat by conduction from his body into the cold water with which his body is in actual contact. A person located in an air-conditioned room loses heat by convention in the air about him, there being conduction of heat from his body into the cold air and continual movement of cold air about him so that there is a continually changing cold air surface in contact with his body. A person who, during a cold day in winter, is located in a heated room adjacent to a cold glass windowpane, loses heat by radiation from his body to the windowpane without contact between his body and the windowpane. Thus, the heating or cooling of a person within an enclosure involves fairly complex interrelationships among various phenomena. To illustrate this complexity, a person during summertime may feel warm at a given indoor air temperature because the windowpanes to which he is adjacent are heated by the hot summer air, whereas the same person during wintertime may feel cool at the same given indoor air temperature because the windowpanes to which he is adjacent are cooled by the cold winter air.
Localized noncontact cooling often is desired in a variety of situations. Thus, for medical purposes, it may be desired to cool all or part of the body of a patient without subjecting him to the discomfort of contact with an ice pack, an alcohol bath or drafty cold air. Or, for energy conservation purposes, it may be desirable to cool a person by a localized noncontact device having a heat transfer capacity in the range of a few hundred BTU's rather than to cool the entire room in which the person is located by a conventional air-conditioning device having a heat transfer capacity in the range of several thousand BTU's. The present invention, features cooling by radiative heat transfer, as opposed to conductive or convective heat transfer.
2. The Prior Art
Prior proposals for producing physiologic cooling by radiant heat exchange have had restricted application. In one prior proposal (U.S. Pat. No. 2,651,503, Sept. 8, 1953, C. A. Mills, System of Radiant Heat Exchanging), interior walls of a room have reflective surfaces which tend to direct infrared radiation to a heat sink with limited intermediate absorption and emission. This system is such that multiple reflections at the walls tend to result in intermediate absorption and emission even if it were possible to maintain high reflectivity of the walls under practical conditions. In another prior proposal (U.S. Pat. No. 3,282,267, Nov. 1, 1966, W. Eidus, Thermoelectric Hypothermia Instrument), cold panels are spaced about the patient in order to establish radiative heat exchange. This system is such that the panels must be unduly large or unduly close to the subject if appreciable radiation exchange is to be achieved. In a more recent proposal (U.S. Pat. No. 4,155,226, May 22, 1979, G. Altman, Infrared Cooler For Restricted Regions), intensified cooling of a restricted region is achieved by utilizing certain principles of geometrical optics to relate the subject region to a large infrared condenser and a small heat sink. The present invention takes advantage of certain mechanical-thermal-optical relationships to provide an infrared radiation cooler that is capable of operating effectively throughout a desired region, without being unduly close to the subject, to produce such physiologic conditions as comfort or hypothermia.